This application claims the priority of Japanese Patent Application No. 2001-96403 filed on Mar. 29, 2001, which is incorporated herein.
1. Field of the Invention
The present invention relates to a damping device. More specifically, the present invention relates to the improvement of the control mechanism of a vibration damping device which uses an electroviscous fluid.
2. Description of the Prior Art
Conventionally, a feeding device which scans a sample in, for example, XYZ directions is employed in a machine such as a coordinate measuring machine, e.g., a three-dimensional coordinate measuring machine, a machine tool or a positioning device. This feeding device allows a supporting column, on which a probe, a tool or the like are provided, to make a feed motion relative to a base, on which normally a sample is mounted, or allows the base to make a feed motion relative to the supporting column, thereby scanning a sample surface.
This feeding device, which is rotatably supported by, for example, the base, includes a rotating object having a male thread provided on a peripheral portion, a nut provided with a female thread fitted into the male thread and the like and fixes the supporting column to the nut. When the rotating object is rotated, the rotating force thereof is transformed into the linear motion of the nut by the male and female threads, whereby the feeding device scans the sample in, for example, a horizontal direction with the supporting column on which the nut is provided set as a base. The use of such a feeding device enables, for example, a three-dimensional coordinate measuring machine to make point-to-point measurement and scanning measurement.
In recent years, much attention has been paid to the scanning measurement of a measuring machine can acquire measurement data in large quantities rather than an improvement in measurement precision. A high speed scanning measuring technique which can shorten measurement time is particularly noted.
However, according to the above-stated feeding device, When the rotating object is rotated, a vibration occurs to the body. While the body is moved at high speed, particularly accelerated and decelerated at, for example, the horizontal position between the base and the supporting column, a hard vibration occurs. In addition, during low speed movement such as during measurement, a micro-vibration different from the vibration during the high speed movement occurs.
These vibrations make it impossible for a machine which employs the feeding device to conduct more precise positioning. Further, these vibrations make it impossible for a measuring machine to make a measurement at a desired measuring point and for a probe to pick up vibrations, thereby obstructing more precise measurement.
In this background, a precision measuring machine such as a three-dimensional coordinate measuring machine is required to be driven at higher speed with weaker vibrations than before.
As a conventional damping method, it has been proposed to provide a damping target relative to a base through a spring. It has been also proposed to add dry friction and viscosity resistance; however all the damping attained thereby acts as traveling load during high speed movement, disadvantageously causing hysteresis.
Furthermore, a method of providing, for example, rubber resin on the connection section between rotation shafts and thereby decreasing the propagation of vibrations has been conventionally proposed. However, if the rubber resin is provided, torsional rigidity deteriorates, which sometimes makes it impossible to surely transmit high torque. As a result, this poses a serious problem in relation to control particularly in the high speed scanning measurement.
Moreover, a residual vibration during high speed movement differs in state from that of during low speed movement. In addition, in case of a measuring machine or the like, a vibration state during point-to-point measurement differs from that of during scanning measurement. Further, a conventional damping device is set to damp a specific vibration state. Due to this, even if there occurs a different vibration state, the conventional damping device is incapable of effectively damping the different vibration state at, for example, a different speed. As a result, it has been conventionally difficult to effectively damp vibrations at varied speeds using a single damping device.
Meanwhile, there has been proposed the following technique (see, for example, Japanese Patent Unexamined Application Publication No. 6-146654 and 1-288612). A feeding device employed in an ordinary mechanical damping device uses an electroviscous fluid in a vibration damper and has a rotation shaft which is rotatably supported in the electroviscous fluid. A voltage to be applied to the electroviscous fluid is changed and the viscosity of the electroviscous fluid is changed, thereby damping a vibration according to each vibration state.
While the damping device using the electroviscous fluid of this type is employed for an ordinary machine, it is also expected to be adapted to a precision machine.
Nevertheless, even with the ordinary mechanical damping device, an electroviscous fluid control method has not been concretely established yet. To apply this method to a precision machine which requires a more precise feed motion and higher speed, it leaves much room for improvement in the high precision and high speed of control.
The present invention has been achieved in view of the conventional problems described above. It is the first object of the present invention to provide a damping device capable of conducting more precise vibration control.
To attain the first object, a damping device according to the present invention is a damping device used in a machine which includes a rotating object rotating about a rotation axis and a motor rotating the rotating object, and characterized by including a vibration damper, a voltage applicator, and a controller.
The vibration damper is filled with an electroviscous fluid having a viscosity changing according to a value of a voltage applied to the electroviscous fluid, and rotatably supports at least a part of the rotating object in the electroviscous fluid.
The voltage applicator applies the voltage to the electroviscous fluid in the vibration damper.
The controller controls an operation of the voltage applicator so that an optimum voltage, at which the viscosity of the electroviscous fluid absorbing a vibration of the rotating object most effectively is obtained, can be applied to the electroviscous fluid in the vibration damper in accordance with a rotating speed of the rotating object.
According to the present invention, the rotating object includes a damping rotation shaft, a driving rotation shaft, and a coupling. In addition, it is preferable that a rotating force from the driving rotation shaft is surely transmitted to the damping rotation shaft through the coupling, and the coupling absorbs misalignment between the damping rotation shaft and the driving rotation shaft.
The damping rotation shaft is supported in the electroviscous fluid in the vibration damper.
The driving rotation shaft transmits a driving force from the motor.
The coupling connects the damping rotation shaft to the driving rotation shaft.
xe2x80x9cA rotating force from the driving rotation shaft is surely transmitted to the damping rotation shaft through the couplingxe2x80x9d indicates that the coupling is made of, for example, a material having high torsional rigidity. The coupling suitably employed in this invention is a coupling which has high torsional rigidity and which can absorb the misalignment between the rotation shafts such as a metal spring type coupling having a metal spring intervened to connect the rotation shafts. This metal spring type coupling is exemplified by a metal coil spring type coupling, a metal plate spring type coupling or the like.
Further, it is the second object of the present invention to provide a damping device capable of conducting vibration control more promptly.
To attain the second object, according to the present invention, the damping device includes an indicator and a memory. In addition, when the indicator indicates the rotating speed of the rotating object, the controller indicates the motor to rotate the rotating object at the indicated rotating speed. Preferably, simultaneously with the indicator, the controller selects the optimum voltage applied to the electroviscous fluid to correspond to the indicated rotating speed and controls the operation of the voltage applicator so that the selected voltage can be applied to the electroviscous fluid in the vibration damper.
The indicator indicates the rotating speed of the rotating object.
The memory stores control information representing a relationship between the rotating speed of the rotating object and the optimum voltage applied to the electroviscous fluid at which the viscosity of the electroviscous fluid absorbing the vibration of the rotating object most effectively at the rotating speed, obtained in advance, for each expected rotating speed of the rotating object.
Further, according to the present invention, the controller preferably selects, from the control information in the memory, the voltage applied to the electroviscous fluid at which the viscosity of the electroviscous fluid in the vibration damper becomes lower as an indicated value of the rotating speed of the rotating object indicated by the indicator becomes higher. On the other hand, the controller preferably selects, from the control information in the memory, the voltage applied to the electroviscous fluid at which the viscosity of the electroviscous fluid in the vibration damper becomes higher as the indicated value of the rotating speed of the rotating object indicated by the indicator becomes lower.
Moreover, according to the present invention, the damping device includes a detector. In addition, it is preferable that the controller selects the optimum voltage applied to the electroviscous fluid to correspond to the rotating speed detected by the detector from the control information in the memory, and actively controls the operation of the voltage applicator so that the selected voltage can be applied to the electroviscous fluid.
The detector detects the rotating speed of the rotating object at real time.
Additionally, according to the present invention, the controller preferably selects the voltage applied to the electroviscous fluid at which the viscosity of the electroviscous fluid in the vibration damper becomes lower as the speed value of the rotating object detected by the detector becomes higher. On the other hand, the controller preferably selects the voltage applied to the electroviscous fluid at which the viscosity of the electroviscous fluid in the vibration damper becomes higher as the speed value of the rotating object detected by the detector becomes lower. It is also preferable that the controller actively controls the operation of the voltage applicator in accordance with the rotating speed detected by the detector.
In addition, to attain the first object, a damping device according to the present invention is a damping device used in a feeding device which includes a rotating object having a male thread formed thereon and rotating about a rotation axis, a motor rotating the rotating object, and a movable object making a linear motion, and characterized by including a vibration damper, a voltage applicator, and a controller.
The vibration damper is provided with a female thread fitted into the male thread of the rotating object and transforming a rotating motion of the rotating object into the linear motion. In addition, the vibration damper is filled with an electroviscous fluid having a viscosity changing in accordance with a value of a voltage applied to the electroviscous fluid, and movably supports at least a part of the movable object in the electroviscous fluid.
The voltage applicator applies the voltage to the electroviscous fluid in the vibration damper.
The controller controls an operation of the voltage applicator so that an optimum voltage, at which the viscosity of the electroviscous fluid absorbing a vibration of the movable object most effectively is obtained, can be applied to the electroviscous fluid in the vibration damper in accordance with a moving speed of the movable object.
To attain the second object, according to the present invention, the damping device includes an indicator and a memory. In addition, it is preferable that when the indicator indicates the moving speed of the movable object, the controller indicates the motor to move the movable object at the indicated moving speed, selects the optimum voltage applied to the electroviscous fluid to correspond to the indicated moving speed and controls the operation of the voltage applicator so that the selected voltage can be applied to the electroviscous fluid in the vibration damper.
The indicator indicates the moving speed of the movable object.
The memory stores control information obtained in advance representing a relationship between the moving speed of the movable object and the optimum voltage applied to the electroviscous fluid at which the viscosity of the electroviscous fluid absorbing the vibration of the movable object most effectively at the moving speed, for each expected moving speed of the movable object.
Furthermore, according to the present invention, the controller preferably selects, from the control information in the memory, the voltage applied to the electroviscous fluid at which the viscosity of the electroviscous fluid in the vibration damper becomes higher as an indicated value of the moving speed of the movable object indicated by the indicator becomes higher. On the other hand, the controller preferably selects, from the control information in the memory, the voltage applied to the electroviscous fluid at which the viscosity of the electroviscous fluid in the vibration damper becomes lower as the indicated value of the moving speed of the movable object indicated by the indicator becomes lower.
Moreover, according to the present invention, the damping device includes a detector. In addition, it is preferable that the controller selects the optimum voltage applied to the electroviscous fluid to correspond to the moving speed detected by the detector from the control information in the memory, and actively controls the operation of the voltage applicator so that the selected voltage can be applied to the electroviscous fluid.
The detector detects the moving speed of the movable object at real time.
Additionally, according to the present invention, the controller preferably selects the voltage applied to the electroviscous fluid at which the viscosity of the electroviscous fluid in the vibration damper becomes higher as the speed value of the movable object detected by the detector becomes higher. On the other hand, the controller preferably selects the voltage applied to the electroviscous fluid at which the viscosity of the electroviscous fluid in the vibration damper becomes lower as the speed value of the movable object detected by the detector becomes lower. It is also preferable that the controller actively controls the operation of the voltage applicator in accordance with the moving speed detected by the detector.